The present invention is directed to a modified phenolic resin composition, method of making same, and an improved adhesive coating composition. More particularly, the present invention is directed to a modified phenolic aldehyde resin composition and method of making same and an improved adhesive coating composition for adhesion of glass fibers to rubber and to the coated glass fiber bundles useful in producing reinforced rubber products.
Fiberous materials have been used extensively as reinforcing material for rubber. The fiberous reinforced rubber products have found use in pneumatic tires, power-drive belts, conveyor belts, timing belts, high-pressure hoses and the like.
Glass fibers in the form of individual fibers, and groups of fibers in the form of strand, roving, cord, rope, fabric and the like are excellent reinforcing materials and give reinforced rubber products good dimensional stability, strength, resiliency and wear. Glass fibers are distinguishable from other fiberous reinforcing materials such as natural and synthetic organic fibers, in that glass fibers do not become elongated or deformed under stress to the extent of other fibers. Unlike other fibers, particular combinations of glass fibers with encapsulating coatings cooperate to yield reinforced materials that have greater strength than either the glass or the coating material alone. While fiberous materials other than glass which are subject to substantial stress elongation are essentially limited in tensile strength to the basic strength of the bare fibers, even if coated, properly coated glass fibers have greater strength than the glass alone.
When glass fibers are used as reinforcing material for rubber, the glass fibers are usually in the form of reinforcing cord or other bundle form, where individual fibers are coated with a size and then brought together into strand. The size is a chemical composition usually containing a coupling agent, such as silane, or Werner complex, a lubricant and other ingredients for handling purposes. The strand or plurality of strands of glass fibers are twisted, intertwisted and/or piled in the conventional manner for cord, yarn, thread formation or other bundle forms. The cord or other bundle forms are coated by dipping or otherwise contacting with a coating mixture containing an elastomeric latex and a homogeneous resin component. Usually the homogeneous resin component is a phenolic aldehyde condensate resin made from resorcinol, formaldehyde and/or phenol. The condensate resin usually has a formaldehyde to phenolic ratio of 0.4 to 0.8 formaldehyde to phenol on a mole basis. Such a resin is characterized by a low degree of polymerization and minimum molecular weight. A particularly useful resorcinol formaldehyde resin with a ratio of 0.6 formaldehyde to 1 resorcinol is sold under the designation Penacolite.RTM. R-2200 resin.
The phenolic aldehyde condensate resins have been produced with many different structures and many additives have been used in the production of the phenolic aldehyde condensate resins. Also, phenolic aldehyde condensate resins have acted as modifiers in the polymerization of other polymers.
In U.S. Pat. No. 2,483,854 (Snyder) modified carbamide (urea) resins are added to overcome the disadvantages of lack of toughness, flexibility and water resistance of the urea-aldehyde resins. The modified carbamide resins consist of a phenol modified urea formaldehyde resin that is particularly useful as a coating and laminating material. The modified carbamide resin is produced by simultaneously reacting a preponderant amount of urea and a smaller amount of thiourea and phenol with formaldehyde. Approximately 10 percent phenol and 10 percent thiourea are used in producing the modified carbamide resin.
In U.S. Pat. No. 3,509,018 (Leshin et al) discloses the use of a resin formed insitu from the reaction of a methylene acceptor and a methylene donor reactible therewith in the production of a rubber and non-metallic reinforced rubber structures. The methylene donor that is used in forming the insitu resin in the rubber being bonded to the surface of the reinforcing agent contains at least a 3 valent nitrogen connected to at least one (--CH.sub.2 --) radical. The remaining valence on the CH.sub.2 radical is connected to an oxy radical (--OX), where x is hydrogen or lower alkyl group. The resin formed insitu from the methylene donor and the methylene acceptor present in the rubber co mpound bonds a rubber component to a polyester or polycarbonate fiber. The laminate of rubber component, insitu formed resin, and polyester or polycarbonate fiber is prepared by coating the rubber onto a fabric of reinforced fibers of polyester or polycarbonate in the usual manner of calendering a coating of the vulcanizable rubber composition onto both sides of the fabric as is done in the conventional manner for coating a tire cord fabric with the tire carcass stock. The reinforcing fabric may be used without any previous treatment and under these conditions fabric is known as gray cord indicating that no treatment in the form of an adhesive composition has been applied for the surface of cord.
In U.S. Pat. No. 3,539,484 and 3,852,232 (Bowman et al) are directed to the production of a resin binder composition by reacting urea-formaldehyde or a thiourea-formaldehyde with a phenol and formaldehyde in the presence of an alkaline catalyst. Generally the phenol to formaldehyde mole ratio added to the initial urea-thiourea-formaldehyde composition is in the range of 1:1 to about 0.25:1. Also all or a part of the phenol used in the composition can be replaced with similar phenolic compounds such as cresol, xylenol, cresylic acid and mixtures thereof. The resin binder composition so produced has an improved chemical structure so that a reduced amount of odor bearing fumes or material is evolved during the curing of the resin binder composition for bonding discrete, inert solid particles such as sand, abrasive grit, wood chips, carbon particles and the like.
In the use of glass fibers as fiberous reinforcing material with a resin latex coating for rubber, it has been suggested to incorporate more individual filaments per unit area in the rubber, which means the packing of the cord or bundle form with glass fibers must be greater. It has been found that in order to facilitate in maintaining the necessary packing, a thicker cord is required, and cords having from 10-15 strands therein have been found to have utility for this purpose. However, this cord with more strands therein produces an effect known as blowholes. A blowhole is caused when cord is cured within a rubber matrix and individual strands, which comprise the cord, have greater adhesion to the rubber matrix than cohesion to themselves. Therefore, the strands separate and pull apart, thus including an air space between the individual strand and the cord. This blowhole phenomenon detracts from the desirable properties that can be obtained in a glass fiber reinforced rubber product having more reinforcement by virtue of incorporating more individual filaments per unit area in the rubber. Therefore, there is a need for an improved phenolic aldehyde resin, and improved phenolic aldehyde latex coating composition to reduce or completely obviate the blowhole phenomenon on any substrate, typically glass fibers.
It is an object of the present invention to provide a modified phenolic aldehyde resin, method of making same, and phenol aldehyde latex adhesive coating for a substrate strand and particularly for glass fiber strand, which is used as a fiberous reinforcement material for rubber, which provides better adhesion between the glass fiber bundles and the rubber, and which reduces the blowhole phenomenon.